1. Field of the Invention
The subject invention relates generally to an antenna. Specifically, the subject invention relates to a frequency-independent broadband antenna, such as a log-periodic antenna, for use in a testing environment.
2. Description of the Related Art
Antenna testing is a necessary step in the process of antenna design and development. The need for comprehensive testing is even more pronounced when testing receiving antennas for vehicles due to the mobility of the receiving antenna and the potential interference caused by vehicle electronic systems, etc.
To accomplish this testing, a transmitting antenna, such as a log-periodic antenna, is used to radiate a radio frequency (RF) signal. The RF signal is received by the receiving antenna and is measured by test equipment. One objective in such testing is to expose the receiving antenna to multiple polarizations across a test frequency range. Vehicle manufacturers and suppliers typically utilize open-site environments and anechoic chambers (i.e., a shielded test environment) to perform this testing. When utilizing an open site environment, the transmitting antenna may be induced to provide multiple polarizations across a test frequency range by changing an overall axis angle of the entire transmitting antenna. However, providing multiple polarizations over the test frequency range is difficult in anechoic chambers since typical anechoic chambers utilize a frequency-sweep field-transmitting system that cannot radiate multiple polarizations by changing the axis angle. Therefore, there is a need for an antenna for providing multiple polarizations over the test frequency range in anechoic chambers or other shielded test environments.
Log-periodic antennas are well known in the prior art. One such antenna is disclosed in U.S. Pat. No. 6,842,156 (the '156 patent). The '156 patent discloses an antenna having a boom extending longitudinally from a front end to a rear end. The antenna also includes a plurality of pairs of elements spaced longitudinally along the boom. The pairs of elements extend laterally from the boom in opposite directions. The length of each element increases from the front end to the rear end of the boom. Spacing between the elements also increases from the front end to the rear end. Several of the longer elements include an outer portion which is bent toward the front end of the antenna. Although several outer portions are bent, the elements remain substantially coplanar. Because the elements are coplanar, the polarization of each frequency is substantially identical and is determined by the overall axis position of the antenna. Unfortunately, the antenna of the '156 patent does not provide the ability to provide multiple polarizations over the test frequency range. Therefore, the antenna of the '156 patent would not be ideal for use in an anechoic chamber to provide multiple polarizations of a test frequency range.
Thus, there remains a need for an antenna and method for providing multiple polarizations over a test frequency range in anechoic chamber and other shielded testing environments.